The present invention relates to a structure for a working machine of a bucket type excavator such as a hydraulic shovel. The present invention also includes a method for producing an arm of a bucket type excavator and the structure for the working machine of the bucket type excavator.
FIG. 1 depicts a hydraulic shovel which is a bucket type excavator. The bucket type excavation machine includes: an upper vehicle body 2 turnably mounted on a lower running body 1, a boom 3 vertically swingably mounted to the upper vehicle body 2, an arm 4 vertically oscillatably mounted to boom 3, and a bucket 5 vertically oscillatably mounted to a tip end of arm 4. A boom cylinder 6 is connected between the upper vehicle body 2 and boom 3. An arm cylinder 7 is connected between boom 3 and arm 4. A bucket cylinder 8 is connected between arm 4 and bucket 5.
During operation of the hydraulic shovel, boom 3 swings vertically, arm 4 and bucket 5 oscillate vertically. Upper vehicle body 2 turns laterally simultaneous with the bucket oscillation, thereby carrying out operations such as excavation and loading to a dump truck.
As shown in FIG. 2, arm 4 includes an arm body 10, an arm cylinder-mounting bracket 11 jointed to one longitudinal end of arm body 10, and a bucket-connection bracket 12 jointed to another longitudinal end of arm body 10.
As shown in FIG. 3, arm body 10 has a hollow and rectangular cross-section comprising an upper lateral plate 13, a lower lateral plate 14 and left and right vertical plates 15, 15.
As shown in FIG. 1, during operation of the excavation machine a vertical load F1, a lateral load F2, a torsion load F3 and the like are applied to arm 4. Durability against these loads is secured by choosing proper dimensional constraints on arm body 10. For example, referring to FIG. 3, load F1 can be stabilized by appropriately choosing dimensions for the arm body cross-sectional width W, cross-sectional height H, as well as appropriately choosing the thicknesses of upper lateral plate 13, lower lateral plate 14 and left and right vertical plates 15, 15. These dimensions and thicknesses are appropriately set in accordance with the magnitude of the loads shown in FIG. 3. In addition, lateral load F2 and torsional load F3 can be compensated for by adding a cross-section restraint member such as a rib 16 shown in FIG. 2.
In hydraulic shovel excavation machines including an upper vehicle body 2 main portion, a boom 3, an arm 4 and a bucket 5, a counter weight 9 is provided at a rear portion of upper vehicle body 2. The amount of counter weight required for the excavation machine depends upon the weight of the machine. For Example, if the working machine is reduced in weight, the weight of the counter weight 9 mounted to the rear portion of the upper vehicle body 2 can be reduced, the rearward projecting amount of the upper vehicle body 2 can be reduced and therefore, a turning radius of the rear end of the upper vehicle body 2 can be reduced.
If the working machine comprising boom 3, arm 4 and bucket 5 is reduced in weight, it is possible to increase the volume of the bucket correspondingly instead of reducing the weight of the counter weight 9 and thus increasing the working amount of the machine.
Further, arm 4 is vertically swung by arm cylinder 7, and a portion of a thrust of arm cylinder 7 supports the weight of arm 4. Therefore, if arm 4 is reduced in weight, the thrust of arm cylinder 7 is effectively utilized as the vertical swinging force of arm 4. Similarly, the weight of arm 4 is applied to boom cylinder 6. Thus, if arm 4 is reduced in weight, the thrust of boom cylinder 6 is effectively utilized.
In generally, when considering the strength of a working machine of the bucket type excavator, as the simplest method, the working machine is replaced with a beam or a thin pipe which is discussed in material mechanics and a strength with respect to the bending and torsion can be evaluated.
That is, the bending stress and shearing stress applied to a cross-section can be obtained by the following general formulas (1) and (2):
"sgr"=M/Zxe2x80x83xe2x80x83(1)
(wherein, "sgr": bending stress on a cross-section, is determined from M; bending moment of a cross-sectional area subject to bending stress, and Z is a cross-section coefficient)
xcfx84=T/(2xc2x7Axc2x7t)xe2x80x83xe2x80x83(2)
(wherein, xcfx84: shearing stress, is determined from T: torsion torque, A: projection area of neutral line of cross-section plate thickness, t: thickness of cross-section plate)
An appropriate shape of the cross-section can be determined from the results of the above calculation and permissible stress of the material to be used. Similarly, deflection of the beam and torsion of the axis can be calculated using general formula of the material mechanics, and such calculation, rigidity of the working machine can also be evaluated.
However, if a working machine designed in accordance with the above evaluation method is actually produced and stress tests are carried out, in many cases the results of the tests are different from the calculated stress values. For this reason, in recent years, stress is evaluated by a computer simulation using finite element method (FEM). Computer simulations result in enhancing the precision in stress evaluations. When stress is calculated using an FEM simulation, it can be found that a cross-sectional area of a working machine, which was previously considered as a beam and axis of material mechanics, is actually changed in shape before and after the load is applied. As a result of this, it is understood that a stress calculated using the general formulas of material mechanics based on the presumption that the shape of a cross-sectional material is not changed and a stress measured during an actual stress test do not coincide with each other.
In the case of a conventionally used working machine having a rectangular cross-section, there are two factors for determining a deformation strength of the cross-section, i.e., rigidity of a rectangular angle portion and rigidity of a rectangular side portion in the outward direction of a surface. When each of the two rigidities do not have sufficient strength, an excessive load applied to the rectangular angle portion causes the cross-section to deform as shown in FIG. 5. To prevent deformation, a cross-section restraint material such as a partition wall is required for a portion in which the cross-section deforms. However, when a cross-section restraint material is provided the productivity of the working machine is lowered.
Referring now to FIG. 3, if the above facts are applied to arm 4 which has a hollow rectangular cross-section, rigidity of the cross-section is determined by bending rigidity of an angle portion (a) and bending rigidity (rigidity in the outward direction of surfaces) of the four surfaces (upper lateral plate 13, lower lateral plate 14, and left and right vertical plates 15 and 15).
That is, influence of the bending rigidity of the surfaces and the bending rigidity of the angle portion is great with respect to the deformation of the cross-section. As shown in FIGS. 3 and 4, when lower plate 14 is fixed and a load F (shown with arrow F) is applied, each of the angled portions (a) are bent and deformed. Upper plate 13, left vertical plate 15 and right vertical plate 15 are bent and deformed in the outward direction of the surfaces (thickness direction). When the thickness of the plate is reduced, reduction of rigidity in the outward direction of the surface is proportional to the third power of a ratio of reduction of the plate thickness.
For the above discussed reasons, if the thickness of each plate is reduced to increase the cross-section of arm 4, the rigidity of the entire boom is largely lowered. As depicted in FIG. 3 with arrows b and c, lateral load F2 and torsion load F3 apply force to arm 4 causing lightweight boom 3 to deform. Therefore, to prevent deformation in the arm, the cross-section must be reinforced in accordance with the above described restraint material such as partition wall 16 and pipe 17. The weight of the boom is increased because of the reinforced cross-section restraint material. The structure of the arm is complicated because of the addition of partition wall 16 and pipe 17. Additionally, there is a problem with producing the excavation machine due to an increase in welding portions.
Furthermore, as shown in FIG. 2, arm 4 is provided with a bucket cylinder bracket 17 for connecting bucket cylinder 8 and a boom cylinder-connection boss 18 for connecting boom 3. If the thickness of each of portions to which these are to be connected (e.g., left and right vertical plates 15, 15 and upper lateral plate 13) is reduced, the rigidity in the outward direction of the surface is lowered. Therefore, in some cases, the deformation in the outward direction of the surface is further increased, the rigidity of arm 4 is reduced, and a deformation (shown with a phantom line in FIG. 3) is produced. Thus, it is difficult to reduce the thickness of the plate material which forms arm body 10.
Further, since the plate members forming the arm body 10 are welded to one another at right angles, if the thickness of the plate members is reduced, the weld jointing efficient is lowered, and it is difficult to secure the durability of the angle joint and thus, it is difficult to reduce the thickness of the plate members forming the arm body 10.
Furthermore, in the case of a conventional boom, upper lateral plate 13, lower lateral plate 14 and left and right vertical plates 15, 15 are formed by cutting them in accordance with the shape of arm body 10. Vehicle arm cylinder bracket 11 and bucket-connection bracket 12 are welded to arm body 10. The method of producing a conventional boom is complicated since: working of each of the plate members is complicated, the welding portion (welding line) is long, and many steps are required to produce the boom.
As shown in FIG. 5, a conventional boom is produced by bending one sheet of a plate (d) into a U-shape. The U-shaped material forms upper lateral plate 13 and left and right vertical plates 15, 15 as a single unit. However, multiple forming steps are required in this case. More specifically, a step for cutting plate d and lower lateral plate 14, a step for bending plate d into a U-shape, and a step for welding two welding portions (welding lines) is required. Thus, many steps are required in manufacturing the conventional boom and this method is complicated.
It is an object of the present invention to provide a structure for a working machine of a bucket type excavator capable of solving the above problem.
It is another object of the present invention to provide a method of producing an arm of a bucket type excavator and a structure for a working machine of a bucket type excavator.
Briefly stated, an arm body of a working machine has a hollow and triangular cross-section. A bucket-connection bracket is jointed to one longitudinal end of an arm body, and an arm cylinder bracket is jointed to another longitudinal end of the arm body, thereby forming an arm. With the triangular cross-sectional structure, the arm body is less prone to deformation under the stress of a load. The improved triangular cross-sectional structure permits the plate thickness of the arm body to be reduced, and the rigidity of the arm body to be increased without mounting a cross-section restraint material in the arm body. The cross-section of the boom will not deform even though the plate thickness is reduced. Therefore, it is possible to reduce the weight of the boom and still prevent deformation of the boom under heavy load. A method of producing an arm body is efficient and simplified since a single sheet of metal may be formed into a triangular shape, with a single welded seem being formed at the seem between abutting edges of the metal material. The various corners of the triangular cross-section may be arc shaped or flat as is desired.
It is an object of the present invention to provide a structure for a bucket-type excavator hydraulic shovel working machine comprising a hollow elongated body, and the elongated body has a substantially triangular shaped cross-section.
It is another object of the present invention to provide a structure for a bucket-type excavator hydraulic shovel working machine comprising: a boom, a bucket, the boom having a tip end side, the boom having a hollow triangular shaped cross-section, and the bucket is mounted to the tip end side of the boom such that the bucket is pivotally supported by the boom.
It is a feature of the invention to provide a method of producing an arm body for a bucket-type excavator working machine, comprising the steps of: bending a plate material having two long sides and two short sides to form a first hollow member with a triangular cross-section, abutting the two long sides of the first hollow member to form butted portions, and welding the butted portions of the two long sides to form butt-welded portion of the arm body.
It is another feature of the invention to provide a method of producing an arm body for a bucket-type excavator working machine, comprising the steps of: bending a plate material having two long sides and two short sides to form a first hollow member with a triangular cross-section, abutting the two long sides of the first hollow member to form butted portions, welding the butted portions of the two long sides to form butt-welded portion of the arm body, where the arm body has a cross-section in which three sides are straight, each straight side is connected to another straight side by a connected portion, each connected portion having an arc shape, the cross-section is a triangular shaped cross-section, the triangular shaped cross-section has a lower surface forming a base side of a triangle, the triangular shaped cross-section has an upper surface formed at a tip of the triangle, and the butt-welded portions of the two long sides are disposed on the lower surface.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.